If one wants to obtain circular-cylindrical bore holes of the quality IT 7 to 8, then one initially drills the hole by means of a twist drill so that it is undersized. Then one bores the hole with a borer and finally one reams the hole with a reamer to the desired diameter and to the desired quality.
This results, with respect to time, the number of tools required, the control of the machine tool, the price/quality relationship and the possibility of defects occurring, in a very high expenditure and a large number of other obvious disadvantages.